Administering an epoch initiated for remote memory access

ABSTRACT

Methods, systems, and products are disclosed for administering an epoch initiated for remote memory access that include: initiating, by an origin application messaging module on an origin compute node, one or more data transfers to a target compute node for the epoch; initiating, by the origin application messaging module after initiating the data transfers, a closing stage for the epoch, including rejecting any new data transfers after initiating the closing stage for the epoch; determining, by the origin application messaging module, whether the data transfers have completed; and closing, by the origin application messaging module, the epoch if the data transfers have completed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims priorityfrom U.S. patent application Ser. No. 11/764,333, filed on Jun. 18,2007, now U.S. Pat. No. 8,296,430, and U.S. patent application Ser. No.13/491,733, filed on Jun. 8, 2012.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.B554331 awarded by the Department of Energy. The Government has certainrights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention is data processing, or, more specifically,methods, systems, and products for administering an epoch initiated forremote memory access.

2. Description of Related Art

The development of the EDVAC computer system of 1948 is often cited asthe beginning of the computer era. Since that time, computer systemshave evolved into extremely complicated devices. Today's computers aremuch more sophisticated than early systems such as the EDVAC. Computersystems typically include a combination of hardware and softwarecomponents, application programs, operating systems, processors, buses,memory, input/output devices, and so on. As advances in semiconductorprocessing and computer architecture push the performance of thecomputer higher and higher, more sophisticated computer software hasevolved to take advantage of the higher performance of the hardware,resulting in computer systems today that are much more powerful thanjust a few years ago.

Parallel computing is an area of computer technology that hasexperienced advances. Parallel computing is the simultaneous executionof the same task (split up and specially adapted) on multiple processorsin order to obtain results faster. Parallel computing is based on thefact that the process of solving a problem usually can be divided intosmaller tasks, which may be carried out simultaneously with somecoordination.

Parallel computers execute parallel algorithms. A parallel algorithm canbe split up to be executed a piece at a time on many differentprocessing devices, and then put back together again at the end to get adata processing result. Some algorithms are easy to divide up intopieces. Splitting up the job of checking all of the numbers from one toa hundred thousand to see which are primes could be done, for example,by assigning a subset of the numbers to each available processor, andthen putting the list of positive results back together. In thisspecification, the multiple processing devices that execute theindividual pieces of a parallel program are referred to as ‘computenodes.’ A parallel computer is composed of compute nodes and otherprocessing nodes as well, including, for example, input/output (‘I/O’)nodes, and service nodes.

Parallel algorithms are valuable because it is faster to perform somekinds of large computing tasks via a parallel algorithm than it is via aserial (non-parallel) algorithm, because of the way modern processorswork. It is far more difficult to construct a computer with a singlefast processor than one with many slow processors with the samethroughput. There are also certain theoretical limits to the potentialspeed of serial processors. On the other hand, every parallel algorithmhas a serial part and so parallel algorithms have a saturation point.After that point adding more processors does not yield any morethroughput but only increases the overhead and cost.

Parallel algorithms are designed also to optimize one more resource thedata communications requirements among the nodes of a parallel computer.There are two ways parallel processors communicate, shared memory ormessage passing. Shared memory processing needs additional locking forthe data and imposes the overhead of additional processor and bus cyclesand also serializes some portion of the algorithm.

Message passing processing uses high-speed data communications networksand message buffers, but this communication adds transfer overhead onthe data communications networks as well as additional memory need formessage buffers and latency in the data communications among nodes.Designs of parallel computers use specially designed data communicationslinks so that the communication overhead will be small but it is theparallel algorithm that decides the volume of the traffic.

Many data communications network architectures are used for messagepassing among nodes in parallel computers. Compute nodes may beorganized in a network as a ‘torus’ or ‘mesh,’ for example. Also,compute nodes may be organized in a network as a tree. A torus networkconnects the nodes in a three-dimensional mesh with wrap around links.Every node is connected to its six neighbors through this torus network,and each node is addressed by its x,y,z coordinate in the mesh. In atree network, the nodes typically are connected into a binary tree: eachnode has a parent, and two children (although some nodes may only havezero children or one child, depending on the hardware configuration). Incomputers that use a torus and a tree network, the two networkstypically are implemented independently of one another, with separaterouting circuits, separate physical links, and separate message buffers.

A torus network lends itself to point to point operations, but a treenetwork typically is inefficient in point to point communication. A treenetwork, however, does provide high bandwidth and low latency forcertain collective operations, message passing operations where allcompute nodes participate simultaneously, such as, for example, anallgather.

Through such data communications networks, one compute node oftenperforms remote memory access on another compute node. The compute nodeinitiating the remote memory access is referred to as the origin computenode, while the compute node which is accessed remotely is referred toas the target compute node. Remote memory access is typically used toprovide passive data synchronization between the origin and the targetcompute nodes. The synchronization is referred to as ‘passive’ becausethe memory access on the target compute node is accomplished using aDirect Memory Access (‘DMA’) subsystem of the target compute node thatrequires little or no involvement of the target compute node'sprocessing core or higher level software applications. Synchronizationbetween the origin and the target compute nodes is effected through theestablishment of a data transfer epoch. An epoch is a time period duringwhich access limitations are placed on data of the target compute node.At the beginning of the epoch, access limitations are placed on thetarget compute node's memory. During the epoch, the origin compute noderemotely accesses memory on the target compute node, reading from orwriting data to the target compute node. At the end of the epoch, theaccess limitations are removed from the target compute node's memory.Until the epoch ends, the origin compute node typically does notcontinue processing its application, and the access limitations on thetarget compute node's memory remain. To close an epoch, all the datatransfers between the origin compute node and the target compute nodemust typically be complete. Advancements for administering such an epochinitiated for remote memory access are described in detail below.

SUMMARY OF THE INVENTION

Methods, systems, and products are disclosed for administering an epochinitiated for remote memory access that include: initiating, by anorigin application messaging module on an origin compute node, one ormore data transfers to a target compute node for the epoch; initiating,by the origin application messaging module after initiating the datatransfers, a closing stage for the epoch, including rejecting any newdata transfers after initiating the closing stage for the epoch;determining, by the origin application messaging module, whether thedata transfers have completed; and closing, by the origin applicationmessaging module, the epoch if the data transfers have completed.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary system for administering an epochinitiated for remote memory access according to embodiments of thepresent invention.

FIG. 2 sets forth a block diagram of an exemplary compute node useful ina parallel computer capable of administering an epoch initiated forremote memory access according to embodiments of the present invention.

FIG. 3A illustrates an exemplary Point To Point Adapter useful insystems capable of administering an epoch initiated for remote memoryaccess according to embodiments of the present invention.

FIG. 3B illustrates an exemplary Global Combining Network Adapter usefulin systems capable of administering an epoch initiated for remote memoryaccess according to embodiments of the present invention.

FIG. 4 sets forth a line drawing illustrating an exemplary datacommunications network optimized for point to point operations useful insystems capable of administering an epoch initiated for remote memoryaccess in accordance with embodiments of the present invention.

FIG. 5 sets forth a line drawing illustrating an exemplary datacommunications network optimized for collective operations useful insystems capable of administering an epoch initiated for remote memoryaccess in accordance with embodiments of the present invention.

FIG. 6 sets forth a block diagram illustrating an exemplarycommunications architecture illustrated as a protocol stack useful inadministering an epoch initiated for remote memory access according toembodiments of the present invention.

FIG. 7 sets forth a flow chart illustrating an exemplary method foradministering an epoch initiated for remote memory access according tothe present invention.

FIG. 8 sets forth a flow chart illustrating a further exemplary methodfor administering an epoch initiated for remote memory access accordingto the present invention.

FIG. 9 sets forth a flow chart illustrating a further exemplary methodfor administering an epoch initiated for remote memory access accordingto the present invention.

FIG. 10 sets forth a flow chart illustrating a further exemplary methodfor administering an epoch initiated for remote memory access accordingto the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary methods, systems, and computer program products foradministering an epoch initiated for remote memory access according toembodiments of the present invention are described with reference to theaccompanying drawings, beginning with FIG. 1. FIG. 1 illustrates anexemplary system for administering an epoch initiated for remote memoryaccess according to embodiments of the present invention. The system ofFIG. 1 includes a parallel computer (100), non-volatile memory for thecomputer in the form of data storage device (118), an output device forthe computer in the form of printer (120), and an input/output devicefor the computer in the form of computer terminal (122). Parallelcomputer (100) in the example of FIG. 1 includes a plurality of computenodes (102).

The compute nodes (102) are coupled for data communications by severalindependent data communications networks including a high speed Ethernetnetwork (174), a Joint Test Action Group (‘JTAG’) network (104), aglobal combining network (106) which is optimized for collectiveoperations, and a torus network (108) which is optimized point to pointoperations. The global combining network (106) is a data communicationsnetwork that includes data communications links connected to the computenodes so as to organize the compute nodes as a tree. Each datacommunications network is implemented with data communications linksamong the compute nodes (102). The data communications links providedata communications for parallel operations among the compute nodes ofthe parallel computer.

In addition, the compute nodes (102) of parallel computer are organizedinto at least one operational group (132) of compute nodes forcollective parallel operations on parallel computer (100). Anoperational group of compute nodes is the set of compute nodes uponwhich a collective parallel operation executes. Collective operationsare implemented with data communications among the compute nodes of anoperational group. Collective operations are those functions thatinvolve all the compute nodes of an operational group. A collectiveoperation is an operation, a message-passing computer programinstruction that is executed simultaneously, that is, at approximatelythe same time, by all the compute nodes in an operational group ofcompute nodes. Such an operational group may include all the computenodes in a parallel computer (100) or a subset all the compute nodes.Collective operations are often built around point to point operations.A collective operation requires that all processes on all compute nodeswithin an operational group call the same collective operation withmatching arguments. A ‘broadcast’ is an example of a collectiveoperation for moving data among compute nodes of an operational group. A‘reduce’ operation is an example of a collective operation that executesarithmetic or logical functions on data distributed among the computenodes of an operational group. An operational group may be implementedas, for example, an MPI ‘communicator.’

‘MPI’ refers to ‘Message Passing Interface,’ a prior art parallelcommunications library, a module of computer program instructions fordata communications on parallel computers. Examples of prior-artparallel communications libraries that may be improved for use withsystems according to embodiments of the present invention include MPIand the ‘Parallel Virtual Machine’ (‘PVM’) library. PVM was developed bythe University of Tennessee, The Oak Ridge National Laboratory, andEmory University. MPI is promulgated by the MPI Forum, an open groupwith representatives from many organizations that define and maintainthe MPI standard. MPI at the time of this writing is a de facto standardfor communication among compute nodes running a parallel program on adistributed memory parallel computer. This specification sometimes usesMPI terminology for ease of explanation, although the use of MPI as suchis not a requirement or limitation of the present invention.

Some collective operations have a single originating or receivingprocess running on a particular compute node in an operational group.For example, in a ‘broadcast’ collective operation, the process on thecompute node that distributes the data to all the other compute nodes isan originating process. In a ‘gather’ operation, for example, theprocess on the compute node that received all the data from the othercompute nodes is a receiving process. The compute node on which such anoriginating or receiving process runs is referred to as a logical root.

Most collective operations are variations or combinations of four basicoperations: broadcast, gather, scatter, and reduce. The interfaces forthese collective operations are defined in the MPI standards promulgatedby the MPI Forum. Algorithms for executing collective operations,however, are not defined in the MPI standards. In a broadcast operation,all processes specify the same root process, whose buffer contents willbe sent. Processes other than the root specify receive buffers. Afterthe operation, all buffers contain the message from the root process.

In a scatter operation, the logical root divides data on the root intosegments and distributes a different segment to each compute node in theoperational group. In scatter operation, all processes typically specifythe same receive count. The send arguments are only significant to theroot process, whose buffer actually contains sendcount*N elements of agiven data type, where N is the number of processes in the given groupof compute nodes. The send buffer is divided and dispersed to allprocesses (including the process on the logical root). Each compute nodeis assigned a sequential identifier termed a ‘rank.’ After theoperation, the root has sent sendcount data elements to each process inincreasing rank order. Rank 0 receives the first sendcount data elementsfrom the send buffer. Rank 1 receives the second sendcount data elementsfrom the send buffer, and so on.

A gather operation is a many-to-one collective operation that is acomplete reverse of the description of the scatter operation. That is, agather is a many-to-one collective operation in which elements of adatatype are gathered from the ranked compute nodes into a receivebuffer in a root node.

A reduce operation is also a many-to-one collective operation thatincludes an arithmetic or logical function performed on two dataelements. All processes specify the same ‘count’ and the same arithmeticor logical function. After the reduction, all processes have sent countdata elements from computer node send buffers to the root process. In areduction operation, data elements from corresponding send bufferlocations are combined pair-wise by arithmetic or logical operations toyield a single corresponding element in the root process's receivebuffer. Application specific reduction operations can be defined atruntime. Parallel communications libraries may support predefinedoperations. MPI, for example, provides the following pre-definedreduction operations:

MPI_MAX maximum MPI_MIN minimum MPI_SUM sum MPI_PROD product MPI_LANDlogical and MPI_BAND bitwise and MPI_LOR logical or MPI_BOR bitwise orMPI_LXOR logical exclusive or MPI_BXOR bitwise exclusive or

In addition to compute nodes, the parallel computer (100) includesinput/output (‘I/O’) nodes (110, 114) coupled to compute nodes (102)through one of the data communications networks (174). The I/O nodes(110, 114) provide I/O services between compute nodes (102) and I/Odevices (118, 120, 122). I/O nodes (110, 114) are connected for datacommunications I/O devices (118, 120, 122) through local area network(LAN') (130). The parallel computer (100) also includes a service node(116) coupled to the compute nodes through one of the networks (104).Service node (116) provides service common to pluralities of computenodes, loading programs into the compute nodes, starting programexecution on the compute nodes, retrieving results of program operationson the computer nodes, and so on. Service node (116) runs a serviceapplication (124) and communicates with users (128) through a serviceapplication interface (126) that runs on computer terminal (122).

As described in more detail below in this specification, the system ofFIG. 1 operates generally to for administering an epoch initiated forremote memory access according to embodiments of the present invention.The system of FIG. 1 operates generally to for administering an epochinitiated for remote memory access according to embodiments of thepresent invention by: initiating, by an origin application messagingmodule on a origin compute node, one or more data transfers to a targetcompute node for the epoch; initiating, by the origin applicationmessaging module after initiating the data transfers, a closing stagefor the epoch, including rejecting any new data transfers afterinitiating the closing stage for the epoch; determining, by the originapplication messaging module, whether the data transfers have completed;and closing, by the origin application messaging module, the epoch ifthe data transfers have completed. Readers will note that the computenode initiating the remote memory access using the data transfers isreferred to as the origin compute node, while the compute node which isaccessed remotely is referred to as the target compute node.

An epoch is a time period during which access limitations are placed ondata of the target compute node while the origin compute node performsremote memory access on the target compute node. At the beginning of theepoch, access limitations are placed on the target compute node'smemory. During the epoch, the origin compute node remotely accessesmemory on the target compute node, reading from or writing data to thetarget compute node. At the end of the epoch, the access limitations areremoved from the target compute node's memory. Until the epoch ends, theorigin compute node typically does not continue processing itsapplication, and the access limitations on the target compute node'smemory remain. To end the epoch, all the data transfers between theorigin compute node and the target compute node must be complete. Theclosing stage of the epoch is the last portion of the epoch during whichno new data transfers are initiated for the epoch. The closing stage ofthe epoch advantageously provides a period of time at the end of theepoch to allow any data transfers currently in progress to completebefore the epoch is closed.

The arrangement of nodes, networks, and I/O devices making up theexemplary system illustrated in FIG. 1 are for explanation only, not forlimitation of the present invention. Data processing systems capable ofadministering an epoch initiated for remote memory access according toembodiments of the present invention may include additional nodes,networks, devices, and architectures, not shown in FIG. 1, as will occurto those of skill in the art. Although the parallel computer (100) inthe example of FIG. 1 includes sixteen compute nodes (102), readers willnote that parallel computers capable of administering an epoch initiatedfor remote memory access according to embodiments of the presentinvention may include any number of compute nodes. In addition toEthernet and JTAG, networks in such data processing systems may supportmany data communications protocols including for example TCP(Transmission Control Protocol), IP (Internet Protocol), and others aswill occur to those of skill in the art. Various embodiments of thepresent invention may be implemented on a variety of hardware platformsin addition to those illustrated in FIG. 1.

Administering an epoch initiated for remote memory access according toembodiments of the present invention may be generally implemented on aparallel computer that includes a plurality of compute nodes. In fact,such computers may include thousands of such compute nodes. Each computenode is in turn itself a kind of computer composed of one or morecomputer processors, its own computer memory, and its own input/outputadapters. For further explanation, therefore, FIG. 2 sets forth a blockdiagram of an exemplary compute node useful in a parallel computercapable of administering an epoch initiated for remote memory accessaccording to embodiments of the present invention. The compute node(152) of FIG. 2 includes one or more computer processors (164) as wellas random access memory (RAM') (156). The processors (164) are connectedto RAM (156) through a high-speed memory bus (154) and through a busadapter (194) and an extension bus (168) to other components of thecompute node (152). Stored in RAM (156) is an application program (158),a module of computer program instructions that carries out parallel,user-level data processing using parallel algorithms. The application(158) of FIG. 2 allocates an application buffer for storing a messagefor transmission to another compute node.

Also stored RAM (156) is an application messaging module (160), alibrary of computer program instructions that carry out parallelcommunications among compute nodes, including point to point operationsas well as collective operations. Application program (158) effects datacommunications with other application running on other compute nodes bycalling software routines in the application messaging module (160). Alibrary of parallel communications routines may be developed fromscratch for use in systems according to embodiments of the presentinvention, using a traditional programming language such as the Cprogramming language, and using traditional programming methods to writeparallel communications routines that send and receive data among nodeson two independent data communications networks. Alternatively, existingprior art libraries may be improved to operate according to embodimentsof the present invention. Examples of prior-art parallel communicationslibraries include the ‘Message Passing Interface’ (‘MPI’) library andthe ‘Parallel Virtual Machine’ (‘PVM’) library.

In the example of FIG. 2, the application messaging module (160)operates generally for administering an epoch initiated for remotememory access according to embodiments of the present invention. Themessaging module (160) of FIG. 2 operates generally for administering anepoch initiated for remote memory access according to embodiments of thepresent invention by: initiating one or more data transfers to a targetcompute node for the epoch; initiating, after initiating the datatransfers, a closing stage for the epoch, including rejecting any newdata transfers after initiating the closing stage for the epoch;determining whether the data transfers have completed; and closing theepoch if the data transfers have completed.

Also stored in RAM (156) is a system messaging module (161) thatimplements system specific protocols for communications that supportmessaging for application (158) and the application messaging module(160). Such system specific protocols are typically invoked through aset of APIs that are exposed to the application messaging module (160).Such system specific protocols used for communications in the systemmessaging module (161) are typically isolated from the application (158)through the application messaging module (160), thus making theinterface provided to the application (158) somewhat independent ofsystem specific details implemented in the system messaging module(161). The system messaging module (161) of FIG. 2 implements systemspecific communications protocols using a set of messaging primitives. Amessaging primitive is a data communications operation that serves as abasic building block for communicating between compute nodes. A messageprimitive may be implemented as, for example, a request to send (‘RTS’)operation that send a RTS control message to a compute node, a clear tosend (‘CTS’) operation that sends a CTS control message to a computenode, a remote get operation that transfers data from one compute nodeto another, a memory FIFO operation that transfers data from one computenode to another, an acknowledgement operation that sends anacknowledgement message to a compute node, and so on. Combining a numberof messaging primitives together forms the basis for developing acommunications protocol. In carrying out system specific communicationsprotocols, the system messaging module (161) typically accessescommunications hardware and software useful according to the presentinvention such as, for example, DMA controller (195), DMA engine (197),and data communications adapters (180, 188).

Also stored in RAM (156) is an operating system (162), a module ofcomputer program instructions and routines for an application program'saccess to other resources of the compute node. It is typical for anapplication program and parallel communications library in a computenode of a parallel computer to run a single thread of execution with nouser login and no security issues because the thread is entitled tocomplete access to all resources of the node. The quantity andcomplexity of tasks to be performed by an operating system on a computenode in a parallel computer therefore are smaller and less complex thanthose of an operating system on a serial computer with many threadsrunning simultaneously. In addition, there is no video I/O on thecompute node (152) of FIG. 2, another factor that decreases the demandson the operating system. The operating system may therefore be quitelightweight by comparison with operating systems of general purposecomputers, a pared down version as it were, or an operating systemdeveloped specifically for operations on a particular parallel computer.Operating systems that may usefully be improved, simplified, for use ina compute node include UNIX™, Linux™, Microsoft XP™, AIX™, IBM's i5/OS™,and others as will occur to those of skill in the art.

The exemplary compute node (152) of FIG. 2 includes severalcommunications adapters (172, 176, 180, 188) for implementing datacommunications with other nodes of a parallel computer. Such datacommunications may be carried out serially through RS-232 connections,through external buses such as USB, through data communications networkssuch as IP networks, and in other ways as will occur to those of skillin the art. Communications adapters implement the hardware level of datacommunications through which one computer sends data communications toanother computer, directly or through a network. Examples ofcommunications adapters useful in systems for administering an epochinitiated for remote memory access according to embodiments of thepresent invention include modems for wired communications, Ethernet(IEEE 802.3) adapters for wired network communications, and 802.11badapters for wireless network communications.

The data communications adapters in the example of FIG. 2 include aGigabit Ethernet adapter (172) that couples example compute node (152)for data communications to a Gigabit Ethernet (174). Gigabit Ethernet isa network transmission standard, defined in the IEEE 802.3 standard,that provides a data rate of 1 billion bits per second (one gigabit).Gigabit Ethernet is a variant of Ethernet that operates over multimodefiber optic cable, single mode fiber optic cable, or unshielded twistedpair.

The data communications adapters in the example of FIG. 2 includes aJTAG Slave circuit (176) that couples example compute node (152) fordata communications to a JTAG Master circuit (178). JTAG is the usualname used for the IEEE 1149.1 standard entitled Standard Test AccessPort and Boundary-Scan Architecture for test access ports used fortesting printed circuit boards using boundary scan. JTAG is so widelyadapted that, at this time, boundary scan is more or less synonymouswith JTAG. JTAG is used not only for printed circuit boards, but alsofor conducting boundary scans of integrated circuits, and is also usefulas a mechanism for debugging embedded systems, providing a convenient“back door” into the system. The example compute node of FIG. 2 may beall three of these: It typically includes one or more integratedcircuits installed on a printed circuit board and may be implemented asan embedded system having its own processor, its own memory, and its ownI/O capability. JTAG boundary scans through JTAG Slave (176) mayefficiently configure processor registers and memory in compute node(152) for use in administering an epoch initiated for remote memoryaccess according to embodiments of the present invention.

The data communications adapters in the example of FIG. 2 includes aPoint To Point Adapter (180) that couples example compute node (152) fordata communications to a network (108) that is optimal for point topoint message passing operations such as, for example, a networkconfigured as a three-dimensional torus or mesh. Point To Point Adapter(180) provides data communications in six directions on threecommunications axes, x, y, and z, through six bidirectional links: +x(181), −x (182), +y (183), −y (184), +z (185), and −z (186).

The data communications adapters in the example of FIG. 2 includes aGlobal Combining Network Adapter (188) that couples example compute node(152) for data communications to a network (106) that is optimal forcollective message passing operations on a global combining networkconfigured, for example, as a binary tree. The Global Combining NetworkAdapter (188) provides data communications through three bidirectionallinks: two to children nodes (190) and one to a parent node (192).

Example compute node (152) includes two arithmetic logic units (‘ALUs’).ALU (166) is a component of processor (164), and a separate ALU (170) isdedicated to the exclusive use of Global Combining Network Adapter (188)for use in performing the arithmetic and logical functions of reductionoperations. Computer program instructions of a reduction routine inparallel communications library (160) may latch an instruction for anarithmetic or logical function into instruction register (169). When thearithmetic or logical function of a reduction operation is a ‘sum’ or a‘logical or,’ for example, Global Combining Network Adapter (188) mayexecute the arithmetic or logical operation by use of ALU (166) inprocessor (164) or, typically much faster, by use dedicated ALU (170).

The example compute node (152) of FIG. 2 includes a direct memory access(‘DMA’) controller (195), which is computer hardware for direct memoryaccess and a DMA engine (197), which is computer software for directmemory access. Direct memory access includes reading and writing tomemory of compute nodes with reduced operational burden on the centralprocessing units (164). A DMA transfer essentially copies a block ofmemory from one compute node to another. While the CPU may initiates theDMA transfer, the CPU does not execute it. In the example of FIG. 2, theDMA engine (197) and the DMA controller (195) support the systemmessaging module (161), and thereby the application message module(160), for administering an epoch initiated for remote memory accessaccording to embodiments of the present invention.

For further explanation, FIG. 3A illustrates an exemplary Point To PointAdapter (180) useful in systems capable of administering an epochinitiated for remote memory access according to embodiments of thepresent invention. Point To Point Adapter (180) is designed for use in adata communications network optimized for point to point operations, anetwork that organizes compute nodes in a three-dimensional torus ormesh. Point To Point Adapter (180) in the example of FIG. 3A providesdata communication along an x-axis through four unidirectional datacommunications links, to and from the next node in the −x direction(182) and to and from the next node in the +x direction (181). Point ToPoint Adapter (180) also provides data communication along a y-axisthrough four unidirectional data communications links, to and from thenext node in the −y direction (184) and to and from the next node in the+y direction (183). Point To Point Adapter (180) in FIG. 3A alsoprovides data communication along a z-axis through four unidirectionaldata communications links, to and from the next node in the −z direction(186) and to and from the next node in the +z direction (185).

For further explanation, FIG. 3B illustrates an exemplary GlobalCombining Network Adapter (188) useful in systems capable ofadministering an epoch initiated for remote memory access according toembodiments of the present invention. Global Combining Network Adapter(188) is designed for use in a network optimized for collectiveoperations, a network that organizes compute nodes of a parallelcomputer in a binary tree. Global Combining Network Adapter (188) in theexample of FIG. 3B provides data communication to and from two childrennodes through four unidirectional data communications links (190).Global Combining Network Adapter (188) also provides data communicationto and from a parent node through two unidirectional data communicationslinks (192).

For further explanation, FIG. 4 sets forth a line drawing illustratingan exemplary data communications network (108) optimized for point topoint operations useful in systems capable of administering an epochinitiated for remote memory access in accordance with embodiments of thepresent invention. In the example of FIG. 4, dots represent computenodes (102) of a parallel computer, and the dotted lines between thedots represent data communications links (103) between compute nodes.The data communications links are implemented with point to point datacommunications adapters similar to the one illustrated for example inFIG. 3A, with data communications links on three axes, x, y, and z, andto and fro in six directions +x (181), −x (182), +y (183), −y (184), +z(185), and −z (186). The links and compute nodes are organized by thisdata communications network optimized for point to point operations intoa three dimensional mesh (105). The mesh (105) has wrap-around links oneach axis that connect the outermost compute nodes in the mesh (105) onopposite sides of the mesh (105). These wrap-around links form part of atorus (107). Each compute node in the torus has a location in the torusthat is uniquely specified by a set of x, y, z coordinates. Readers willnote that the wrap-around links in the y and z directions have beenomitted for clarity, but are configured in a similar manner to thewrap-around link illustrated in the x direction. For clarity ofexplanation, the data communications network of FIG. 4 is illustratedwith only 27 compute nodes, but readers will recognize that a datacommunications network optimized for point to point operations for usein administering an epoch initiated for remote memory access inaccordance with embodiments of the present invention may contain only afew compute nodes or may contain thousands of compute nodes.

For further explanation, FIG. 5 sets forth a line drawing illustratingan exemplary data communications network (106) optimized for collectiveoperations useful in systems capable of administering an epoch initiatedfor remote memory access in accordance with embodiments of the presentinvention. The example data communications network of FIG. 5 includesdata communications links connected to the compute nodes so as toorganize the compute nodes as a tree. In the example of FIG. 5, dotsrepresent compute nodes (102) of a parallel computer, and the dottedlines (103) between the dots represent data communications links betweencompute nodes. The data communications links are implemented with globalcombining network adapters similar to the one illustrated for example inFIG. 3B, with each node typically providing data communications to andfrom two children nodes and data communications to and from a parentnode, with some exceptions. Nodes in a binary tree (106) may becharacterized as a physical root node (202), branch nodes (204), andleaf nodes (206). The root node (202) has two children but no parent.The leaf nodes (206) each has a parent, but leaf nodes have no children.The branch nodes (204) each has both a parent and two children. Thelinks and compute nodes are thereby organized by this datacommunications network optimized for collective operations into a binarytree (106). For clarity of explanation, the data communications networkof FIG. 5 is illustrated with only 31 compute nodes, but readers willrecognize that a data communications network optimized for collectiveoperations for use in systems for administering an epoch initiated forremote memory access in accordance with embodiments of the presentinvention may contain only a few compute nodes or may contain thousandsof compute nodes.

In the example of FIG. 5, each node in the tree is assigned a unitidentifier referred to as a ‘rank’ (250). A node's rank uniquelyidentifies the node's location in the tree network for use in both pointto point and collective operations in the tree network. The ranks inthis example are assigned as integers beginning with 0 assigned to theroot node (202), 1 assigned to the first node in the second layer of thetree, 2 assigned to the second node in the second layer of the tree, 3assigned to the first node in the third layer of the tree, 4 assigned tothe second node in the third layer of the tree, and so on. For ease ofillustration, only the ranks of the first three layers of the tree areshown here, but all compute nodes in the tree network are assigned aunique rank.

For further explanation, FIG. 6 sets forth a block diagram illustratingan exemplary communications architecture illustrated as a protocol stackuseful in administering an epoch initiated for remote memory accessaccording to embodiments of the present invention. The exemplarycommunications architecture of FIG. 6 sets forth two compute nodes, anorigin compute node (600) and a target compute node (601). The exampleof FIG. 6 only illustrates two compute nodes for ease of explanation andnot for limitation. In fact, administering an epoch initiated for remotememory access according to embodiments of the present invention may beimplemented using an origin node and any number of target compute nodesas is often the case with very large scale computer systems such asparallel computers with thousands of compute nodes.

The exemplary communications architecture of FIG. 6 includes anapplication layer (602) composed of application (158) installed on theorigin compute node (600) and application (604) installed on the targetcompute node (601). Data communications between applications (158, 604)are effected using application messaging modules (160, 608) installed oneach of the compute nodes (600, 601). Applications (158, 604) maycommunicate messages by invoking function of an application programminginterfaces (API') exposed by the application messaging modules (160,608). For the origin compute node's application (158) to transmitmessages to the target compute node's application (604), the origincompute node's application (158) typically calls a ‘send’ messagingfunction of the application messaging module (160), while the targetcompute node's application (604) typically calls a ‘receive’ messagingfunction of the application messaging module (608). Each application(158, 604) provides match data to their respective application messagingmodule (160, 608), the origin compute node's application (158) providingorigin match data and the target compute node's application (604)providing target match data.

Match data is the data used by the application messaging layer (610) tomatch the ‘send’ function called by the origin compute node'sapplication (604) with the ‘receive’ function called by the targetcompute node's application (158) so that the data specified in the‘send’ function is stored in the location specified in the ‘receive’function. Match data may be implemented, for example, as a datastructure specifying the origin compute node's unique rank in theoperational group, a tag number provided by the application, and acontext that identifies the particular operational group of computenodes involved in the transfer. Match data provided to the origincompute node's application messaging module (608) is referred to asorigin match data, while the match data provided to the target computenode's application messaging module (160) is referred to as target matchdata.

The exemplary communications architecture of FIG. 6 includes anapplication messaging layer (610) that provides a hardware-independentmessaging interface that supports messaging in the application layer(602). Such a messaging interface is typically utilized by applications(158, 604) in the application layer (602) through a set of APIs exposedby application messaging modules. In the example of FIG. 6, themessaging layer (610) is composed of an application messaging module(160) installed on the origin compute node (600) and an applicationmessaging module (608) installed on the target compute node (601).

In the example of FIG. 6, the application messaging module (160)operates for administering an epoch initiated for remote memory accessaccording to embodiments of the present invention. The epoch istypically initiated upon request by the application (158) on the origincompute node (600) through the API of the application message module(160). The application creates a unique identifier for the epoch andprovides the identifier to the application messaging module (160) alongwith the rank of the target compute node (601) involved in thesynchronization. The application messaging module (160) initiates one ormore data transfers to the target compute node (601) for the epoch.After initiating the data transfers, the application messaging module(160) initiates a closing stage for the epoch. As mentioned above, theclosing stage of the epoch is the last portion of the epoch during whichno new data transfers are initiated for the epoch. The closing stage ofthe epoch advantageously provides a period of time at the end of theepoch to allow any data transfers currently in progress to completebefore the epoch is closed. After initiating the closing stage for theepoch, the application messaging module (160) rejects any new datatransfers and determines whether the previously initiated data transfershave completed. The application messaging module (160) then closes theepoch if the data transfers have completed.

The exemplary communications architecture of FIG. 6 includes a systemmessaging layer (614) that implements hardware-specific protocols forcommunications that support messaging in the application layer (602) andthe application messaging layer (610). Such system specific protocolsare typically invoked through a set of APIs that are exposed to theapplication messaging layer (610). Such system specific protocols usedfor communications in the system messaging layer (614) are typicallyisolated from the application layer (602) through the applicationmessaging layer (610), thus making the interface provided to theapplication layer (602) somewhat independent of system-specific detailsimplemented in the system messaging layer (614). In the example of FIG.6, the system messaging layer (614) is composed of a system messagingmodule (161) installed on the origin compute node (600) and a systemmessaging module (616) installed on the target compute node (601).

The system messaging layer (614) of FIG. 6 implements system specificcommunications protocols using a set of messaging primitives. Amessaging primitive is a data communications operation that serves as abasic building block for communicating between compute nodes. A messageprimitive may be implemented as, for example, a request to send (‘RTS’)operation that send a RTS control message to a compute node, a clear tosend (‘CTS’) operation that sends a CTS control message to a computenode, a remote get operation that transfers data from one compute nodeto another, a memory FIFO operation that transfers data from one computenode to another, an acknowledgement operation that sends anacknowledgement message to a compute node, and so on. Combining a numberof messaging primitives together forms the basis for developing acommunications protocol. In carrying out system specific communicationsprotocols, the system messaging layer (614) typically accessescommunications hardware and software useful according to the presentinvention such as, for example, DMA controllers, DMA engines, datacommunications hardware, and so on.

The exemplary communications architecture of FIG. 6 also includes ahardware layer (634) that defines the physical implementation and theelectrical implementation of aspects of the hardware on the computenodes such as the bus, network cabling, connector types, physical datarates, data transmission encoding and may other factors forcommunications between the compute nodes (600 and 601) on the physicalnetwork medium. The hardware layer (634) of FIG. 6 is composed ofcommunications hardware (636) of the origin compute node (600),communications hardware (638) of the target compute node (601), and thedata communications network (108) connecting the origin compute node(600) to the target compute node (601). Such communications hardware mayinclude, for example, point-to-point adapters and DMA controllers asdescribed above with reference to FIGS. 2 and 3A. In the example of FIG.6, the communications hardware (636 and 638) each include a transmissionstack (640 and 644) for storing network packets for transmission toother communications hardware through the data communications network(108), and each include a reception stack (642 and 646) for storingnetwork packets received from other communications hardware through thedata communications network (108).

The exemplary communications architecture of FIG. 6 illustrates a DMAengine (197) for the origin compute node (600) and a DMA engine (620)for the target compute node (601). The DMA engines (197 and 620) in theexample of FIG. 6 are illustrated in both the system messaging layer(614) and the hardware layer (634). The DMA engines (197 and 620) areshown in both the system messaging layer (614) and the hardware layer(634) because a DMA engine useful in embodiments of the presentinvention may often provide system messaging layer interfaces and alsoimplement communications according to some aspects of the communicationhardware layer (634). The exemplary DMA engines (197 and 620) of FIG. 6each include an injection FIFO buffer (628 and 632) for storing datadescriptors (618) for messages to be sent to other DMA engines on othercompute nodes using a memory FIFO data transfer operation or direct putdata transfer operation. The exemplary DMA engines (197 and 620) of FIG.6 each also include a reception FIFO buffer (626 and 630) for storingdata descriptors (618) for messages received from other DMA engines onother compute nodes. Although FIG. 6 only illustrates a single injectionFIFO buffer and a single reception FIFO buffer, readers will note that aDMA engine may have access to any number of injection FIFO buffers andreception FIFO buffers for carrying out data transfers from an origincompute node to a target compute node according to embodiments of thepresent invention.

A memory FIFO data transfer operation is a mode of transferring datausing a DMA engine on an origin node and a DMA engine on a target node.In a memory FIFO data transfer operation, data is transferred along witha data descriptor describing the data from an injection FIFO for theorigin DMA engine to a target DMA engine. The target DMA engine in turnsplaces the descriptor in the reception FIFO and caches the data. A coreprocessor then retrieves the data descriptor from the reception FIFO andprocesses the data in cache either by instructing the DMA to store thedata directly or carrying out some processing on the data, such as evenstoring the data by the core processor.

A direct put operation is a mode of transferring data using a DMA engineon an origin node and a DMA engine on a target node. A direct putoperation allows data to be transferred and stored on the target computenode with little or no involvement from the target node's processor. Toeffect minimal involvement from the target node's processor in thedirect put operation, the origin DMA transfers the data to be stored onthe target compute node along with a specific identification of astorage location on the target compute node. The origin DMA knows thespecific storage location on the target compute node because thespecific storage location for storing the data on the target computenode has been previously provided by the target DMA to the origin DMA.

For further explanation, FIG. 7 sets forth a flow chart illustrating anexemplary method for administering an epoch initiated for remote memoryaccess according to the present invention. The example of FIG. 7includes an origin compute node (600) and a target compute node (601).The origin compute node (600) of FIG. 7 has installed upon it an originapplication messaging module (160) capable of carry out the method foradministering an epoch initiated for remote memory access according tothe present invention.

The method of FIG. 7 includes initiating (700), by the origin messagingmodule (160), an epoch (712) for remote memory access. The originmessaging module (160) initiates (700) the epoch (712) for remote memoryaccess according to the method of FIG. 7 in response to receiving arequest from an application on the origin compute node (600) through anAPI exposed by the origin messaging module (160). Through the API, theapplication may provide the origin messaging module (160) with anidentifier for the epoch (712), which the origin messaging module (160)combines with the rank of the origin compute node (600) to uniquelyidentify the epoch (712) in the operational group for the compute nodes(600 and 601). In addition to providing an epoch identifier, theapplication also provides the origin messaging module (160) with therank of the target compute node (601) included in the epoch (712). Inthe method of FIG. 7, the origin messaging module (160) may initiate(700) an epoch (712) for remote memory access by sending an epochinitialization message to the target compute node (601) that instructsthe target compute node (601) to place access limitations on the targetcompute node's memory.

The method of FIG. 7 also includes initiating (702), by an originapplication messaging module (160) on an origin compute node (600), oneor more data transfers (701) to a target compute node (601) for theepoch (712). Readers will note that FIG. 7 only illustrates one datatransfer for explanation and clarity. However, any number of datatransfers may be initiated before initiating the closing stage (714) forthe epoch (712) according to embodiments of the present invention. Thedata transfer (701) of FIG. 7 retrieves data from the target computenode (601) and stores the data on the origin compute node (600). In theexample of FIG. 7, the data transfer (701) is effected using a getoperation (706). A get operation (706) is a DMA-assisted data transferoperation that allows an origin compute node to retrieve data from atarget compute node with minimal involvement from the processor on thetarget compute node providing the data. The origin application messagingmodule (160) may initiate (702) the transfer (701) to a target computenode (601) for the epoch (712) according to the method of FIG. 7 bysending a remote get message (707) to the target compute node (601). Theremote get message (707) of FIG. 7 typically specifies the location onthe target compute node (601) where the data to be transferred is storedand specifies where the transferred data may be stored on the origincompute node (600) by origin compute node's DMA engine as the dataarrives on the origin compute node (600). Upon receiving the remote getmessage (707), a DMA engine on the target compute node (601) begins thedata transfer (701) by reading the data from storage on the targetcompute node (601), packetizing the data into network packets andtransmitting the data through a data communication network to the origincompute node (600).

In the method of FIG. 7, initiating (702), by the origin applicationmessaging module (160) on an origin compute node (600), one or more datatransfers (701) to a target compute node (601) for the epoch (712)includes incrementing (704) a get counter (708) upon initiation of theget operation (706) for each data transfer (701). The get counter (708)is a counter that keeps track of how many data transfers are currentlyin progress to the target compute node (601) for the epoch (712). In theexample of FIG. 7, the get counter (708) keeps track of how many datatransfers are currently in progress to the target compute node (601) forthe epoch (712) using a value (710).

The method of FIG. 7 also includes initiating (716), by the originapplication messaging module (160) after initiating the data transfers(701), a closing stage (714) for the epoch (712), including rejectingany new data transfers after initiating the closing stage (714) for theepoch (712). The closing stage (714) of the epoch (712) is the lastportion of the epoch (712) during which no new data transfers areinitiated for the epoch (712). The closing stage (714) of the epoch(712) advantageously provides a period of time at the end of the epoch(712) to allow any data transfers currently in progress to completebefore the epoch (712) is closed. In the method of FIG. 7, the originapplication messaging module (160) initiates (716) the closing stage(714) for the epoch (712) before the data transfer (701) is complete.

The method of FIG. 7 includes determining (718), by the originapplication messaging module (160), whether the data transfers (701)have completed. The origin application messaging module (160) maydetermine (718) whether the data transfers (701) have completedaccording to the method of FIG. 7 by determining whether the value (710)of the get counter (708) is zero. If the value (710) of the get counter(708) is zero, then the data transfer (701) has completed because avalue of zero indicates that there are not data transfer currently inprogress for the epoch (712). If the value (710) of the get counter(708) is not zero, then the data transfer (701) has not completedbecause a non-zero value indicates that data transfer are currently inprogress for the epoch (712).

The method of FIG. 7 includes waiting (720), by the origin applicationmessaging module (160), for completion of the data transfer (701) if thedata transfer (701) has not been completed. The origin applicationmessaging module (160) may wait (720) for completion of the datatransfer (701) according to the method of FIG. 7 by listening for atransfer completion signal from the DMA engine of the origin computenode (600) indicating that a data transfer for the epoch (712) iscomplete.

The method of FIG. 7 also includes decrementing (722), by the originapplication messaging module (160), the get counter (708) uponcompletion of each get operation (706). The origin application messagingmodule (160) may decrement (722) the get counter (708) upon completionof each get operation (706) according to the method of FIG. 7 afterreceiving transfer completion signal from the DMA engine of the origincompute node (600) indicating that a data transfer for the epoch (712)is complete. After decrementing (722) the get counter (708), the methodof FIG. 7 again determines (718) whether the data transfers (701) havecompleted as described above.

The method of FIG. 7 includes closing (724), by the origin applicationmessaging module (160), the epoch (712) if the data transfers (701) havecompleted. The origin application messaging module (160) may close (724)the epoch (712) according to the method of FIG. 7 by sending an epochtermination message to the target compute node (601) that instructs thetarget compute node (601) to remove any access limitations on the targetcompute node's memory and by returning processor control to the origincompute node's application requesting the synchronization with thetarget compute node (601).

As mentioned above, the application messaging module (160) initiates(716) a closing stage (714) for an epoch (712) before the data transfer(701) is completed in the example of FIG. 7. Because there are pendingdata transfers for the epoch (712) when the closing stage (714) isinitiated, the duration of the closing stage (714) is at least as longas the time taken to complete any remaining data transfers. Uponcompletion of the remaining data transfers, the application messagingmodule (160) of FIG. 7 may close (724) epoch (712).

In FIG. 7, the origin application messaging module initiates a closingstage for an epoch before all of the data transfers initiated for theepoch are complete. In some embodiments, however, the origin applicationmessaging module may initiate a closing stage for an epoch after all ofthe data transfers initiated for the epoch are complete. For furtherexplanation, therefore, FIG. 8 sets forth a flow chart illustrating afurther exemplary method for administering an epoch initiated for remotememory access according to the present invention in which the originapplication messaging module (160) initiates (716) a closing stage (714)for an epoch (712) after the data transfers are complete.

The method of FIG. 8 is similar to the method of FIG. 7. That is, themethod of FIG. 8 includes: initiating (700), by the origin messagingmodule (160), an epoch (712) for remote memory access; initiating (702),by an origin application messaging module (160) on an origin computenode (600), one or more data transfers (701) to a target compute node(601) for the epoch (712), including incrementing (704) a get counter(708) upon initiation of the get operation (706) for each data transfer(701); decrementing (722), by the origin application messaging module(160), the get counter (708) upon completion of each get operation(706); initiating (716), by the origin application messaging module(160) after initiating the data transfer (701), a closing stage (714)for the epoch (712), including rejecting any new data transfers afterinitiating the closing stage (714) for the epoch (712); determining(718), by the origin application messaging module (160), whether thedata transfers (701) have completed; and closing (724), by the originapplication messaging module (160), the epoch (712) if the datatransfers (701) have completed.

As mentioned above, the application messaging module (160) initiates(716) a closing stage (714) for an epoch (712) after the data transfer(701) is completed in the example of FIG. 8. Because there are nopending data transfer operations for the epoch (712) when the closingstage (714) is initiated, the duration of the closing stage (714)illustrated in FIG. 8 is minimal, and the application messaging module(160) may close (724) epoch (712) shortly after initiating the closingstage (714).

Readers will note that the data transfers described with reference toFIGS. 7 and 8 are effected using get operations that allows an origincompute node to retrieve data from a target compute node. A datatransfer, however, may also be effected using a put operation. A putoperation is a DMA-assisted transfer operation that allows an origincompute node to store data on a target compute node with minimalinvolvement from the processor on the target compute node. For furtherexplanation, therefore, FIG. 9 sets forth a flow chart illustrating afurther exemplary method for administering an epoch initiated for remotememory access according to the present invention in which the datatransfer is effected using a put operation. The example of FIG. 9includes an origin compute node (600) and a target compute node (601).The origin compute node (600) of FIG. 9 has installed upon it an originapplication messaging module (160), and the target compute node (601) ofFIG. 9 has installed upon it a target application messaging module(160). In the example of FIG. 9, each application messaging module (160and 608) is capable of carry out the method for administering an epochinitiated for remote memory access according to the present invention.

The method of FIG. 9 includes initiating (700), by the origin messagingmodule (160), an epoch (712) for remote memory access. The originmessaging module (160) initiates (700) the epoch (712) for remote memoryaccess according to the method of FIG. 9 in response to receiving arequest from an application on the origin compute node (600) through anAPI exposed by the origin messaging module (160). Through the API, theapplication may provide the origin messaging module (160) with anidentifier for the epoch (712), which the origin messaging module (160)combines with the rank of the origin compute node (600) to uniquelyidentify the epoch (712) in the operational group for the compute nodes(600 and 601). In addition to providing an epoch identifier, theapplication also provides the origin messaging module (160) with therank of the target compute node (601) included in the epoch (712). Inthe method of FIG. 9, the origin messaging module (160) may initiate(700) an epoch (712) for remote memory access by sending an epochinitialization message to the target compute node (601) that instructsthe target compute node (601) to place access limitations on the targetcompute node's memory.

The method of FIG. 9 also includes initiating (702), by an originapplication messaging module (160) on an origin compute node (600), oneor more data transfers (701) to a target compute node (601) for theepoch (712). Readers will note that FIG. 9 only illustrates one datatransfer for explanation and clarity. However, any number of datatransfers may be initiated before initiating the closing stage (714) forthe epoch (712) according to embodiments of the present invention. Thedata transfer (701) of FIG. 9 transfers data stored on the origincompute node (600) to the target compute node (601). In the example ofFIG. 9, the data transfer (701) is effected using a put operation (908).The origin application messaging module (160) may initiate (702) thetransfer (701) to a target compute node (601) for the epoch (712)according to the method of FIG. 9 by invoking a direct put operationthat specifies the location on the target compute node (601) where thedata is to be stored. Upon invoking a direct put operation, a DMA engineon the origin compute node (600) begins the data transfer (701) byreading the data from storage on the origin compute node (600),packetizing the data into network packets and transmitting the datathrough a data communication network to the DMA engine of the targetcompute node (601).

In the method of FIG. 9, initiating (702), by the origin applicationmessaging module (160) on an origin compute node (600), one or more datatransfers (701) to a target compute node (601) for the epoch (712)includes incrementing (900) a put counter (902) upon initiation of theput operation (908) for each data transfer (701). The put counter (902)of FIG. 9 is a counter that keeps track of how many data transfers theorigin compute node has initiated for the epoch (712). In the example ofFIG. 9, the put counter (902) keeps track of how many data transfers theorigin compute node has initiated for the epoch (712) using a value(904).

The method of FIG. 9 also includes initiating (716), by the originapplication messaging module (160) after initiating the data transfers(701), a closing stage (714) for the epoch (712), including rejectingany new data transfers after initiating the closing stage (714) for theepoch (712). As mentioned above, the closing stage (714) of the epoch(712) is the last portion of the epoch (712) during which no new datatransfers are initiated for the epoch (712). The closing stage (714) ofthe epoch (712) advantageously provides a period of time at the end ofthe epoch (712) to allow any data transfers currently in progress tocomplete before the epoch (712) is closed. In the method of FIG. 9, theorigin application messaging module (160) initiates (716) the closingstage (714) for the epoch (712) before the data transfer (701) iscomplete.

Initiating (716), by the origin application messaging module (160) afterinitiating the data transfers (701), a closing stage (714) for the epoch(712) according to the method of FIG. 9 includes sending (906) a value(904) of the put counter (902) to the target compute node (601). Theorigin application messaging module (160) may send (906) a value (904)of the put counter (902) to the target compute node (601) according tothe method of FIG. 9 by encapsulating the value (904) of the put counter(902) in a message and transmitting the message to the target computenode (601).

The method of FIG. 9 includes determining (920), by the targetapplication messaging module (608), whether the value (904) of the putcounter (902) matches a value (918) of a got counter (916). The gotcounter (916) of FIG. 9 is a counter that keeps track of how many datatransfers have completed on the target compute node (601) for the epoch(712). In the example of FIG. 9, the got counter (916) keeps track ofhow many data transfers have completed on the target compute node (601)for the epoch (712) using a value (918). If the value (904) of the putcounter (902) is the same as the value (918) of the got counter (916),then the value (904) of the put counter (902) matches the value (918) ofthe got counter (916) and the number of data transfers initiated by theorigin compute node (600) matches the number of data transfer completedon the target compute node (601). If the value (904) of the put counter(902) is not the same as the value (918) of the got counter (916), thenthe value (904) of the put counter (902) does not match the value (918)of the got counter (916) and the number of data transfers initiated bythe origin compute node (600) does not match the number of data transfercompleted on the target compute node (601), indicating that there aresome remaining data transfer that have yet to complete.

The method of FIG. 9 includes waiting (912), by the target applicationmessaging module (608), for completion of the data transfer (701) if thevalue (904) of the put counter (902) does not match the value (918) ofthe got counter (916). The target application messaging module (608) maywait (912) for completion of the data transfer (701) according to themethod of FIG. 9 by listening for a transfer completion signal from theDMA engine of the target compute node (601) indicating that a datatransfer for the epoch (712) is complete.

The method of FIG. 9 includes incrementing (914), by a targetapplication messaging module (608) on the target compute node (601), agot counter (916) upon completion of each put operation (908). Thetarget application messaging module (608) may increment (914) the gotcounter (916) upon completion of each put operation (908) according tothe method of FIG. 9 after receiving transfer completion signal from theDMA engine of the target compute node (601) indicating that a datatransfer for the epoch (712) is complete. After incrementing (914) thegot counter (916), the method of FIG. 9 again determines (920) whetherthe value (904) of the put counter (902) matches a value (918) of a gotcounter (916) as described above.

The method of FIG. 9 also includes sending (922), by the targetapplication messaging module (608) to the origin application messagingmodule (160), a completion acknowledgement (910) if the value (904) ofthe put counter (902) matches the value (918) of the got counter (916).The completion acknowledgement (910) of FIG. 9 indicates that all of thedata transfers initiated on the origin compute node (600) have completedon the target compute node (601). The target application messagingmodule (608) may send (922) the completion acknowledgement (910) to theorigin application messaging module (160) according to the method ofFIG. 9 by encapsulating the completion acknowledgement (910) in amessage and transmitting the message to the origin compute node (600).

The method of FIG. 9 includes determining (718), by the originapplication messaging module (160), whether the data transfers (701)have completed. The origin application messaging module (160) maydetermine (718) whether the data transfers (701) have completedaccording to the method of FIG. 9 by determining whether the completionacknowledgement has been received in the origin compute node (600). Ifthe completion acknowledgement has been received in the origin computenode (600), then the data transfers (701) have completed because all ofthe data transfers initiated on the origin compute node (600) havecompleted on the target compute node (601). If the completionacknowledgement has not been received in the origin compute node (600),then the data transfers (701) have not completed because some of thedata transfers initiated on the origin compute node (600) have yet to becompleted on the target compute node (601).

The method of FIG. 9 includes closing (724), by the origin applicationmessaging module (160), the epoch (712) if the data transfers (701) havecompleted. The origin application messaging module (160) may close (724)the epoch (712) according to the method of FIG. 9 by sending an epochtermination message to the target compute node (601) that instructs thetarget compute node (601) to remove any access limitations on the targetcompute node's memory and by returning processor control to the origincompute node's application requesting the synchronization with thetarget compute node (601).

As mentioned above, the application messaging module (160) initiates(716) a closing stage (714) for an epoch (712) before the data transfer(701) is completed. Because there are pending data transfers for theepoch (712) when the closing stage (714) is initiated, the duration ofthe closing stage (714) is at least as long as the time taken tocomplete any remaining data transfers and for the origin compute node(600) to receive the completion acknowledgement (910). Upon completionof the remaining data transfers and reception by the origin compute node(600) of the completion acknowledgement (910), the application messagingmodule (160) of FIG. 9 may close (724) epoch (712).

In FIG. 9, the origin application messaging module initiates a closingstage for an epoch before all of the data transfers initiated for theepoch using a put operation are complete. In some embodiments, however,the origin application messaging module may initiate a closing stage foran epoch using a put operation after all of the data transfers initiatedfor the epoch are complete. For further explanation, therefore, FIG. 10sets forth a flow chart illustrating a further exemplary method foradministering an epoch initiated for remote memory access according tothe present invention in which the origin application messaging module(160) initiates (716) a closing stage (714) for an epoch (712) after thedata transfers are complete.

The method of FIG. 10 is similar to the method of FIG. 9. That is, themethod of FIG. 10 includes: initiating (700), by the origin messagingmodule (160), an epoch (712) for remote memory access; initiating (702),by an origin application messaging module (160) on an origin computenode (600), one or more data transfers (701) to a target compute node(601) for the epoch (712), including incrementing (900) a put counter(902) upon initiation of the put operation (908) for each data transfer;incrementing (914), by a target application messaging module (608) onthe target compute node (601), a got counter (916) upon completion ofeach put operation (908); initiating (716), by the origin applicationmessaging module (160) after initiating the data transfers (701), aclosing stage (714) for the epoch (712), including rejecting any newdata transfers after initiating the closing stage (714) for the epoch(712) and sending (906) a value (904) of the put counter (902) to thetarget compute node (601); determining (920), by the target applicationmessaging module (608), whether the value (904) of the put counter (902)matches a value (918) of the got counter (916); sending (922), by thetarget application messaging module (608) to the origin applicationmessaging module (160), a completion acknowledgement (910) if the value(904) of the put counter (902) matches the value (918) of the gotcounter (916); determining (718), by the origin application messagingmodule (160), whether the data transfers (701) have completed; andclosing (724), by the origin application messaging module (160), theepoch (712) if the data transfers (701) have completed.

As mentioned above, the application messaging module (160) initiates(716) a closing stage (714) for an epoch (712) after the data transfer(701) is completed. Because there are no pending data transferoperations for the epoch (712) when the closing stage (714) isinitiated, the duration of the closing stage (714) is at least as longas the period of time required for the value of the put counter (902) toreach the target compute node (601) and have the target compute nodereturn a completion acknowledgement (910) to the origin compute node(600). After receiving the completion acknowledgement (910), theapplication messaging module (160) may close (724) the epoch (712).

Exemplary embodiments of the present invention are described largely inthe context of a fully functional computer system for administering anepoch initiated for remote memory access. Readers of skill in the artwill recognize, however, that the present invention also may be embodiedin a computer program product disposed on computer readable media foruse with any suitable data processing system. Such computer readablemedia may be transmission media or recordable media for machine-readableinformation, including magnetic media, optical media, or other suitablemedia. Examples of recordable media include magnetic disks in harddrives or diskettes, compact disks for optical drives, magnetic tape,and others as will occur to those of skill in the art. Examples oftransmission media include telephone networks for voice communicationsand digital data communications networks such as, for example,Ethernets™ and networks that communicate with the Internet Protocol andthe World Wide Web as well as wireless transmission media such as, forexample, networks implemented according to the IEEE 802.11 family ofspecifications. Persons skilled in the art will immediately recognizethat any computer system having suitable programming means will becapable of executing the steps of the method of the invention asembodied in a program product. Persons skilled in the art will recognizeimmediately that, although some of the exemplary embodiments describedin this specification are oriented to software installed and executingon computer hardware, nevertheless, alternative embodiments implementedas firmware or as hardware are well within the scope of the presentinvention.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A method of administering an epoch initiated forremote memory access, the method comprising: initiating, by an originapplication messaging module on an origin compute node, one or more datatransfers to a target compute node for the epoch; initiating, by theorigin application messaging module after initiating the data transfers,a closing stage for the epoch, including rejecting any new datatransfers after initiating the closing stage for the epoch and prior toclosing the epoch; closing, by the origin application messaging module,the epoch after the data transfers have completed; wherein: each datatransfer is effected using a put operation; initiating, by an originapplication messaging module on a origin compute node, one or more datatransfers to a target compute node for the epoch further comprisesincrementing a put counter upon initiation of the put operation for eachdata transfer; the method further comprises incrementing, by a targetapplication messaging module on the target compute node, a got counterupon completion of each put operation; and initiating, by the originapplication messaging module after initiating the data transfers, aclosing stage for the epoch further comprises sending a value of the putcounter to the target compute node.
 2. The method of claim 1 whereininitiating, by the origin application messaging module after initiatingthe data transfers, a closing stage for the epoch further comprisesinitiating the closing stage for the epoch before the data transfers arecomplete.
 3. The method of claim 1 wherein initiating, by the originapplication messaging module after initiating the data transfers, aclosing stage for the epoch further comprises initiating the closingstage for the epoch after the data transfers are completed.
 4. Themethod of claim 1 wherein: each data transfer is effected using a getoperation; initiating, by an origin application messaging module on aorigin compute node, one or more data transfers to a target compute nodefor the epoch further comprises incrementing a get counter uponinitiation of the get operation for each data transfer; the methodfurther comprises decrementing, by the origin application messagingmodule, the get counter upon completion of each get operation; anddetermining, by the origin application messaging module, whether thedata transfers have completed further comprises determining whether avalue of the get counter is zero.
 5. The method of claim 1, wherein themethod further comprises: determining, by the target applicationmessaging module, whether the value of the put counter matches a valueof the got counter, and sending, by the target application messagingmodule to the origin application messaging module, a completionacknowledgement if the value of the put counter matches the value of thegot counter; and determining, by the origin application messagingmodule, whether the data transfers have completed further comprisesdetermining whether the completion acknowledgement has been received inthe origin compute node.
 6. The method of claim 1 wherein the origincompute node and the target compute node are comprised in a parallelcomputer, the parallel computer comprising a plurality of compute nodesconnected for data communications through a data communications network,the data communications network optimized for point to point datacommunications.
 7. A system capable of administering an epoch initiatedfor remote memory access, the system comprising: one or more computerprocessors; computer memory operatively coupled to the computerprocessors, the computer memory having disposed within it computerprogram instructions capable of: initiating, by an origin applicationmessaging module on an origin compute node, one or more data transfersto a target compute node for the epoch; initiating, by the originapplication messaging module after initiating the data transfers, aclosing stage for the epoch, including rejecting any new data transfersafter initiating the closing stage for the epoch and prior to closingthe epoch; closing, by the origin application messaging module, theepoch after the data transfers have completed; wherein: each datatransfer is effected using a put operation; initiating, by an originapplication messaging module on a origin compute node, one or more datatransfers to a target compute node for the epoch further comprisesincrementing a put counter upon initiation of the put operation for eachdata transfer; the computer memory also has disposed within it computerprogram instructions capable of incrementing, by a target applicationmessaging module on the target compute node, a got counter uponcompletion of each put operation; and initiating, by the originapplication messaging module after initiating the data transfers, aclosing stage for the epoch further comprises sending a value of the putcounter to the target compute node.
 8. The system of claim 7 whereininitiating, by the origin application messaging module after initiatingthe data transfers, a closing stage for the epoch further comprisesinitiating the closing stage for the epoch before the data transfers arecomplete.
 9. The system of claim 7 wherein initiating, by the originapplication messaging module after initiating the data transfers, aclosing stage for the epoch further comprises initiating the closingstage for the epoch after the data transfers are completed.
 10. Thesystem of claim 7 wherein: each data transfer is effected using a getoperation; initiating, by an origin application messaging module on aorigin compute node, one or more data transfers to a target compute nodefor the epoch further comprises incrementing a get counter uponinitiation of the get operation for each data transfer; the computermemory also has disposed within it computer program instructions capableof decrementing, by the origin application messaging module, the getcounter upon completion of each get operation; and determining, by theorigin application messaging module, whether the data transfers havecompleted further comprises determining whether a value of the getcounter is zero.
 11. The system of claim 7, wherein the computer memoryalso has disposed within it computer program instructions capable of:determining, by the target application messaging module, whether thevalue of the put counter matches a value of the got counter, andsending, by the target application messaging module to the originapplication messaging module, a completion acknowledgement if the valueof the put counter matches the value of the got counter; anddetermining, by the origin application messaging module, whether thedata transfers have completed further comprises determining whether thecompletion acknowledgement has been received in the origin compute node.12. The system of claim 7 wherein the origin compute node and the targetcompute node are comprised in a parallel computer, the parallel computercomprising a plurality of compute nodes connected for datacommunications through a data communications network, the datacommunications network optimized for point to point data communications.13. A computer program product for administering an epoch initiated forremote memory access, the computer program product comprising a computerreadable non-transmission medium, the computer readable non-transmissionmedium comprising computer program instructions capable of: initiating,by an origin application messaging module on an origin compute node, oneor more data transfers to a target compute node for the epoch;initiating, by the origin application messaging module after initiatingthe data transfers, a closing stage for the epoch, including rejectingany new data transfers after initiating the closing stage for the epochand prior to closing the epoch; closing, by the origin applicationmessaging module, the epoch after the data transfers have completed;wherein: each data transfer is effected using a put operation;initiating, by an origin application messaging module on a origincompute node, one or more data transfers to a target compute node forthe epoch further comprises incrementing a put counter upon initiationof the put operation for each data transfer; the computer programproduct further comprises computer program instructions capable ofincrementing, by a target application messaging module on the targetcompute node, a got counter upon completion of each put operation; andinitiating, by the origin application messaging module after initiatingthe data transfers, a closing stage for the epoch further comprisessending a value of the put counter to the target compute node.
 14. Thecomputer program product of claim 13 wherein initiating, by the originapplication messaging module after initiating the data transfers, aclosing stage for the epoch further comprises initiating the closingstage for the epoch before the data transfers are complete.
 15. Thecomputer program product of claim 13 wherein initiating, by the originapplication messaging module after initiating the data transfers, aclosing stage for the epoch further comprises initiating the closingstage for the epoch after the data transfers are completed.
 16. Thecomputer program product of claim 13 wherein: each data transfer iseffected using a get operation; initiating, by an origin applicationmessaging module on a origin compute node, one or more data transfers toa target compute node for the epoch further comprises incrementing a getcounter upon initiation of the get operation for each data transfer; thecomputer program product further comprises computer program instructionscapable of decrementing, by the origin application messaging module, theget counter upon completion of each get operation; and determining, bythe origin application messaging module, whether the data transfers havecompleted further comprises determining whether a value of the getcounter is zero.
 17. The computer program product of claim 13 whereinthe computer program product further comprises computer programinstructions capable of: determining, by the target applicationmessaging module, whether the value of the put counter matches a valueof the got counter, and sending, by the target application messagingmodule to the origin application messaging module, a completionacknowledgement if the value of the put counter matches the value of thegot counter; and determining, by the origin application messagingmodule, whether the data transfers have completed further comprisesdetermining whether the completion acknowledgement has been received inthe origin compute node.
 18. The computer program product of claim 13wherein the origin compute node and the target compute node arecomprised in a parallel computer, the parallel computer comprising aplurality of compute nodes connected for data communications through adata communications network, the data communications network optimizedfor point to point data communications.